(1) Field of the Invention
The invention relates to a method of applying a durable process mark to a product, more particularly glass.
A process mark in the sense of the invention means a marking which is applied to a product, and the process mark on the product is read out in a further method by means of sensors, more particularly optical sensors, and the product is then aligned precisely into a predetermined position on the basis of the information obtained from the process mark.
The application of these kinds of process marks is vital to virtually all production sequences. In the case of automation, the marks applied to the product help to ensure, for optical sensors, continuous procedural monitoring and control in the production operations.
For a variety of reasons, these process marks are difficult to apply in a defined position. Remedies to date have often involved notches, projections, grooves and, for example, printed markings, which are then scanned mechanically or optically and used for orientation.
The marks are frequently applied by methods based on the copying of a single repeat. Such methods include rotational and intermittent marking operations, with the consequence that the marks are at an equal distance from one another.
(2) Description of Related Art
Process marks are used for monitoring and control, for the purpose, for example, of the automatic positioning of printing plates. In order to apply the individual colours in a positionally accurate way relative to one another in multi-colour printing, each printing plate prints an accompanying mark onto the print substrate. The positions of the process marks with the individual colours, also called register marks, are detected and compared with one another. This provides information on the positioning of the printing plate relative to the substrate, and is used as a basis for the precise orientation of the printing plates.
Process marks are frequently used to allow workpieces to be joined in a particular orientation. For this purpose, computer-assisted detection and orientation systems are used, in which the method is applied repeatedly to the continually recorded camera images of the process marks, also known as adjustment marks or positioning marks, until the positioning of the workpieces is correct.
A disadvantage of the known process marks is that they are usually produced in an intermittent operation, as for example in a printing process, and hence that only identical content can be applied. For example, at regular intervals on a continuous web, control marks are applied in the form of a rectangle. These control marks are recognized by a detection system and hence trigger a variety of operations—for example, the web is folded or slit.
In the assembly of appliances, moreover, process marks are used to provide the individual components with the correct orientation relative to one another. There again, an optical device captures the control mark. The device records deviations between the current position of the article and its desired position, and so the article is guided accordingly. The process mark thus contains only information concerning a position. Possible further information in the control mark, such as tolerances and quality of the components, that could be taken into account in downstream operations, is unknown.
The process marks ought typically to consist of a suitable material to rule out                unwanted parting of the applied mark from the article;        the scribing running, being wiped, or becoming illegible due to abrasion or lightening, and/or        the functionality of the article being compromised.        